1. Field of the Invention
The present invention relates to an engagement structure of a connecting shell wherein the connecting shell is coupled with a clutch drum for united rotation thereof in an automatic transmission.
2. Description of the Prior Art
An automatic transmission has been put into practice which is constructed by adapting a torque converter to a gear change mechanism including a planetary gear device. Such an automatic transmission is mounted on an automobile for example to release a driver from a complicated clutch operation.
A gear change mechanism in the example of the automatic transmission of an automobile comprises rotary members such as planetary gears, a clutch, a brake, and a main shaft, and coupling members such as a connecting shell for connecting these rotary devices mutually.
The connecting shell is to couple two or more of rotary members for united rotation thereof around a main shaft. Although there is known a case where the two rotary members are united integrally with facing ends of one connecting shell, in view of convenience of designing or assembling a mechanism, there is another case where the rotary device and the connecting shell are engaged with the aid of an engagement structure. In the latter, torque is transmitted through the engagement therebetween in the direction of rotation thereof, and in contrast they can be driven to slide axially for separation thereof.
Although the engagement structure is, as disclosed in Japanese Laid-Open Patent Publication No. 63-246542, applicable to a coupling portion between a clutch drum and the connecting shell, it may be applied to coupling devices and rotary members other than the foregoing members or to coupling portions between rotary members.
The engagement structure of the conecting shell at the coupling portion with the clutch drum includes many grooves which are forced by cutting out the end of the cylindrical external periphery of the clutch drum axially at an equal interval, and many protrusions which are formed by cutting out the circumferential part of the connecting shell radially at an equal interval. The conecting shell and the clutch drum are intersecting each other, having the protrusions of the connecting shell be engaged with the grooves of the clutch drum.
In the following, the engagement structure of the connecting shell disclosed in the aforementioned Japanese Laid-Open Patent Publication No. 63-246542 will be described with reference to FIGS. 4 and 5.
Referring to FIGS. 4 and 5 there are illustrated a partial sectional view of an automatic transmission, and an axial view illustrating the engagement structure when viewed from the left side of FIG. 4.
Herein, a reverse clutch drum 31 and a connecting shell 32 are coupled with each other through an engagement structure 30 for transmittal of torque.
As illustrated in FIG. 4, the automatic transmission is constructed by combining a torque converter 36 contained in a converter housing 39A with a gear change mechanism 38 contained in a transmission casing 39B. The transmission casing 39B and the converter housing 39A are securely fixed to each other with the aid of a plurality of bolts not illustrated. The torque converter 36 serves to transmit driving force inputted from an engine located at the right but not illustrated into an input shaft 35 to a main shaft 33 of the gear change mechanism 38. An oil pump 37 supported by the converter housing 39A at the center of the same serves to circulate oil to a torque converter 36 as well as to produce high pressure oil required for the control of the gear change mechanism 38.
A main part, not illustrated, of the gear change mechanism is disposed further at the left side of the connecting shell 32 disposed at the left end of FIG. 4. The main part comprises a plurality of stages of planetary gears, clutches other than those illustrated in the figure, a brake, a hydraulic control mechanism, a mechanism for transmitting a gear rotation output to the output shaft of the gear change mechanism 38, and a bearing mechanism for the main shaft 33, etc.
A reverse clutch drum 31 of the gear change mechanism 38 is a united inner-outer press drum, which is constructed by drawing a steel plate into a doughnut shape and forming an external periphery thereof into a cylindrical shape and which includes an inner drum 31H fixed to the inside thereof. There are formed a spline for holding a clutch plate on the side of an entrance of the inner drum 31H and formed a hydraulic cylinder disposed on a bottom side. In an annular space inside the reverse clutch drum 31 there are stored a member constituting the reverse clutch and a clutch (high clutch) of another set. Between the inner drum 31H and the high clutch 34 there are closely assembled inner and outer clutch plates, a retaining plate, a piston, and a spring, etc., these members constituting the reverse clutch drum. A cylinder end of the reverse clutch drum 31 is connected with an outer edge of the connecting shell 32 through the engagement structure 30.
The connecting shell 32, that is a disk-shaped member formed by drawing a steel sheet, is disposed so as to intersect a cylindrical outer periphery of the reverse clutch drum 31. The connecting shell 32 connects the reverse clutch drum 31 and the planetary gear disposed at the left side but not illustrated and rotates them integrally. In the engagement structure 30, the protrusions 32A formed on the outer periphery of the connecting shell 32 are engaged with many grooves formed radially in the reverse clutch drum 31 at the end of the same. Between the reverse clutch drum 31 and the connecting shell 32 torque, i.e., rotary force around the main shaft 33 is transmitted through the engagement. In contrast, upon disassembly/assembly only left sliding of the connecting shell 32 along the main shaft 33 ensures rapid removal/achievement of the engagement between the reverse clutch drum 31 and the connecting shell 32.
In the engagement structure 30 surrounded by a broken line in FIG. 5, the reverse clutch drum 31 includes a groove 31B formed by cutting out the cylinder end of the cylindrical outer periphery perpendicularly to the paper surface at an equal interval. An edge of the protrusion 31A left behind after the groove 31B is formed abuts an edge of the protrusion 32A and transmits torque. Upon disassemby/assembly, the engagement state is rapidly released/completed by forcing the connecting shell 32 to slide in the direction of the upper portion/back surface of the paper. It is noted here that in FIG. 5 a gap between the protrusion 32A and the protrusion 31A is exaggerated for convenience of the illustration. Actually, for avoiding shocking abutment the protrusions 31A is loosely held over the full width of the grooves 32A.
However, the conventional engagement structure of the connecting shell has the following difficulties.
In the conventional engagement structure 30 illustrated in FIGS. 4 and 5, transmittal of torque between the connecting shell 32 and the reverse clutch drum 31 is achieved only at the abutment part between the protrusion 32A and the protrusion 31A illustrated in FIG. 5. More specifically, there is transmitted torque which is obtained multiplying a total area (a).times.(n), (a) an area of the abutment part (force reception area) in one engagement structure 30 and (n) the number of the protrusions 32A, by pressure (p) applied to the abutment part and by (r) a radius of the abutment part. There is accordingly increased the pressure (p) onto the abutment part when the transmitting torque through the connecting shell 32 is increased as an output of the automatic transmission is increased or when miniaturization of the gear change mechanism 38 is attempted by way of reducing the diameter of the reverse clutch drum 31.
Particularly, the reverse clutch has a greater speed reduction ratio to hereby operate at a reverse range where large torque is outputted so that the pressure (p) applied to the abutment part between the connecting shell 32 and the reverse clutch drum 31 is originally considerably larger even though the engagement structure 30 is located outward.
The increase of the pressure (p) increases a wear rate of the abutment part in the engagement structure 30 to shorten the lives of the connecting shell 32 and the reverse clutch drum 31. The further increase of the pressure (p) causes compression breaking of the abutment part in the engagement strucutre 30 and buckling deformations of the protrusions 32A and the protrusions 31A. It is therefore necessary to increase the total area (a).times.(n) of the abutment part for preventing the pressure (p) from being increased when it is intended to increase the foregoing transmitting torque or to miniaturize the gear change mechanism 38.
Since the area (a) of the abutment part in one engagement structure 30 is a product of the thickness of the connecting shell 32 and the thickness of the reverse clutch drum 31, an increase of one or both of the connecting shell 32 and the reverse clutch drum 31 ensures an increase of the total force reception area.
However, the increased thickness of the connecting shell 32 requires displacement of the locations of rotary components and coupling components of the gear change mechanism 32 stacked axially along the main shaft 33, needing great alteration of the conventional design.
The increased thickness further makes difficult pressing of the connecting shell 32 and hence increases the cost of the pressing. And it is necessary to extend the reverse clutch drum axially, which is disadvantageous for shortening the entire length of the automatic transmission.
Increasing of the thickness of the reverse clutch drum 31 causes the weight of the reverse clutch drum 31 to be increased and opposes the intent of making the automatic transmission light weight. Also, it has the severe demerits in view of the material cost and the processing cost.